A communications system is a facility which enables communication between two or more entities such as user terminal equipment and/or network entities as the nodes associated with a communication system. The communication may comprise, for example, communication of voice, electronic mail (email), text messages, etc.
The communication may be provided by a fixed line and/or wireless communication interface. A feature of wireless communication systems is that they provide mobility for the users thereof. An example of communications systems providing wireless communication are public land mobile networks (PLMN). An example of the fixed line system is a public switched telephone network (PSTN).
A communications system typically operates in accordance with a given standard or specification which sets out what the various elements of the system are permitted to do and how that should be achieved. For example, the standard or specification may define if the user, or more precisely user equipment, is provided with a circuit switched service or a packet switched service or both. Communication protocols and/or parameters which should be used for the connection also are typically defined. For example, the manner in which communication should be implemented between the user and the elements of the communication network is typically based on a predefined communication protocol. In other words, a specific set of “rules” on which the communication can be based need to be defined to enable to communication.
So-called “multi-homed” mobile devices (user equipment) have been proposed where IP (internet protocol) connectivity via access networks may appear and disappear due to mobility of the user equipment. For example, a multi-homed user equipment may be arranged to be capable of accessing a WLAN (wireless local area network) and a GPRS network (general packet radio service). A WLAN network is generally a localised network, for example run in the context of an office environment whereas the GPRS network is a public land mobile network. Typically, when the user equipment is in the office environment it is preferred that the user equipment accesses the WLAN network but when the user equipment leaves the office environment the user equipment accesses the GPRS network.
When the user equipment moves for example from the WLAN network to the GPRS network, or vice versa, the user equipment IP (Internet Protocol) address will change. The applications that are running in the user equipment can use a mobility service (such as mobile IP, if the network infrastructure is supported) or the application can manage connection breaks itself by reconnecting sockets after the moving from one network to another.
If the user equipment application has chosen to use a mobility service, such as Mobile IP, it may occur that a home agent (HA) is not reachable because the HA server is down or for example an internet link between the user equipment and the home agent server is down. This causes a problem that the applications running on the user equipment will not be able to automatically keep their source IP address unchanged and the sockets unbroken, if for example the user equipment moves from one network to another. Applications using mobile IP make the assumption that the mobility service works at all times and do not have the ability to cope with the problem caused by the home agent being unreachable. This results in a bad user experience.
In more detail, the mobility service, such as mobile IP is normally used on top of a packet switched connection, such as IP. When the HA server is not reachable, the mobile IP implementation deactivates itself on the packet processing path of the user equipment TCP/IP (Transport control protocol/Internet Protocol) stack. In this case, the client application was able to continue using an IP connection if it was still working. However, it was not possible for the user equipment to resume the desired mobility service as it brings a seamless service to UE. Furthermore, because the mobile IP connection is broken, the IP address of the application was changed resulting in the existing sockets being broken without prior notice. This results in a breaking or discontinuity in a service being used by the user equipment.
It is therefore an aim of at least some embodiments of the present invention to address or at least mitigate one or more of the problems described.